Just because a test tool is designed to meet the safety standards for test and measurement equipment doesn’t guarantee that the tool actually meets those safety requirements. Only trust test tools that have been independently tested and proven to meet the standards.
It may sound logical that, as long as you choose a multimeter with a high enough voltage rating for the measurement you’re about to take, your safety should be assured. But we all know this isn’t so. Besides the accidents that happen when someone subjects a meter to a higher voltage than what it’s rated for, there is also the possibility of high-voltage spikes or transients being present, whether from internal fluctuations based on the operation of other components or from external lightning strikes.
Two of the standards that are most often used in the test and measurement world include the International Electrotechnical Commission (IEC) standards and Conformite Europeenne (CE) standards. Compliance to either of these standards is no doubt important when you go to buy your product. In fact, IEC goes so far as to create specific measurement categories from Cat. I for protected equipment like computers and other electronics to Cat. IV for three-phase utility connections close to the primary overcurrent protection equipment. Even these specifications can be misunderstood if the user doesn’t read up on transient test values for each category. For example, a Cat. II meter may be rated at a working voltage of 1,000 V but can only handle a peak impulse transient of 6,000 V, whereas a Cat. IV meter rated at a working voltage of only 600 V can actually handle a peak impulse transient of 8,000 V.
But here’s the important part of this discussion: Although test tool manufacturers go through a lot to design to such standards, in the long run, they are only standards. IEC and CE are just proposed standards, suggested directives. Neither IEC nor CE is responsible for enforcing the standards they set up. In fact, the manufacturers of multimeters and other testing equipment self-certify that they meet the proposed standards. These companies issue a declaration of conformity and mark their own products using the IEC or CE symbol.
So what should a user look for? The best way to ensure the safety of a test and measurement tool for use at your facility is to look for the symbol and listing number of an independent testing laboratory such as UL (Underwriters Laboratories), CSA (Canadian Standards Association), TUV (Technical Inspection Association), or other recognized testing laboratory. In these instances, the symbol of the entity can only be used if the product successfully completed testing to the agency’s standards. Note that agencies like UL actually base their standards on other national and international standards. For example UL 3111 is based on the IEC 1010 standard. Making sure your test or measurement tool bears the symbol of at least one or more of these independent testing agencies is the only way to ensure that the tool was actually tested for safety compliance. Your tool shouldn’t just be designed to meet safety standards. It should meet and, preferably, exceed the standards’ requirements for safety.